how to get data length in bytes in notification only characteristics without enabling notification

RE: how to get data length in bytes in notification only characteristics without enabling notification

Andy — Mon, 23 Apr 2018 06:29:14 GMT

No, each characteristic has its own p_data, so it doesn't matter if you receive data from another characteristic. And yes, essentially you should have an array(per characteristic) big enough to hold the maximum amount of data that you can receive from a characteristic. Those things should be documented somewhere in the peripheral's API. If you don't have access to that, making each array size 20 will be the safest bet. You are already using 512 bytes in your previous implementation, so I guess RAM is not a limitation for you.

RE: how to get data length in bytes in notification only characteristics without enabling notification

nikunj8086 — Mon, 23 Apr 2018 06:19:51 GMT

hi andy,

thanks for reply. so the array will be used as spi register table by user and will be accessed by used via spi interface. and array index will be register address.

i like your idea but problem is that *p_data pointer is pointing to received data from ble and will be changed if another characteristic will send data to central device. so what i will do is that i will make p_data as array of size 20 because my ble data has maximum length of 20 bytes and copy ble data to it.

RE: how to get data length in bytes in notification only characteristics without enabling notification

Andy — Mon, 23 Apr 2018 05:25:51 GMT

Ah, I understand. Is there any particular reason why you decided to implement it that way? That is a very bad, error prone architecture.

May I suggest you use something like this?

typedef struct {
	uint16_t uuid;
	uint8_t * p_data;
} notification_data_t

static notification_data_t notification[NUM_OF_CHARACTERISTICS];

RE: how to get data length in bytes in notification only characteristics without enabling notification

nikunj8086 — Mon, 23 Apr 2018 05:17:14 GMT

hi andy,

i am not using any memory allocation,

basically i have a array of uint16_t type with length of 0xFF,

i only want to reserve space in array for all the characteristics, and after that, that particuler array area will be used to store data from same characteristics.

for example

0x00 reserved
0x01 char1 uuid
0x02 char1 data1
0x03 char1 data2
0x04 char2 uuid
0x05 char2 data1
0x06 char2 data2

so when i will receive data from char 1 i will store only on it's reserved location on array.

RE: how to get data length in bytes in notification only characteristics without enabling notification

Andy — Sun, 22 Apr 2018 19:05:06 GMT

I don't understand how you're planning to create that table. What do you mean with "allocate address"? Are you using malloc and the heap?

RE: how to get data length in bytes in notification only characteristics without enabling notification

nikunj8086 — Sun, 22 Apr 2018 15:48:47 GMT

hi andy,

so basically i have to create a register table where all the data will be stored.

now to store that data i need to know the exact data size to allocate address of current characteristic and next characteristic

example:

address content on that address

0x0001 first char uuid

0x0002 first char data

0x0003 second char uuid

0x0004 second char data

i am using nordic thingy 52 as periphreal for testing, in that most services are notification only. and notification only be sent to central device on any event. like buttun service.

RE: how to get data length in bytes in notification only characteristics without enabling notification

Andy — Sun, 22 Apr 2018 14:55:28 GMT

Why do you need to know the data length if notifications are not enabled?